Gestational length assignment based on last menstrual period, first trimester crown-rump length, ovulation, and implantation timing

Abstract

PurposeUnderstanding the natural length of human pregnancy is central to clinical care. However, variability in the reference methods to assign gestational age (GA) confound our understanding of pregnancy length. Assignation from ultrasound measurement of fetal crown-rump length (CRL) has superseded that based on last menstrual period (LMP). Our aim was to estimate gestational length based on LMP, ultrasound CRL, and implantation that were known, compared to pregnancy duration assigned by day of ovulation.MethodsProspective study in 143 women trying to conceive. In 71 ongoing pregnancies, gestational length was estimated from LMP, CRL at 10–14 weeks, ovulation, and implantation day. For each method of GA assignment, the distribution in observed gestational length was derived and both agreement and correlation between the methods determined.ResultsMedian ovulation and implantation days were 16 and 27, respectively. The gestational length based on LMP, CRL, implantation, and ovulation was similar: 279, 278, 276.5 and 276.5 days, respectively. The distributions for observed gestational length were widest where GA was assigned from CRL and LMP and narrowest when assigned from implantation and ovulation day. The strongest correlation for gestational length assessment was between ovulation and implantation (r = 0.98) and weakest between CRL and LMP (r = 0.88).ConclusionsThe most accurate method of predicting gestational length is ovulation day, and this agrees closely with implantation day. Prediction of gestational length from CRL and known LMP are both inferior to ovulation and implantation day. This information could have important implications on the routine assignment of gestational age.

Nausea and vomiting in pregnancy is not just ‘morning sickness’: data from a prospective cohort study in the UK

“…11,12 Day of ovulation provides the most accurate method for determining pregnancy duration. 13 hCG was measured (AutoDELFIA, Perkin Elmer) in late luteal phase and throughout early pregnancy in order to identify viable pregnancy and early pregnancy loss.…”

Estimated date of delivery based on second trimester fetal head circumference: A population‐based validation of 21 451 deliveries

“…15,16 Delayed ovulation could imply a gestational length beyond 280 days, but this was not the case in a study of 59 women with a known ovulation time. Ovulation and conception were thought to happen around day 14 of the menstrual cycle, but recent studies found a median length of the follicular phase of 16 days.…”

“…Ovulation and conception were thought to happen around day 14 of the menstrual cycle, but recent studies found a median length of the follicular phase of 16 days. 15,16 Delayed ovulation could imply a gestational length beyond 280 days, but this was not the case in a study of 59 women with a known ovulation time. 16 Other clinical and large epidemiological studies, however, found a median gestational length based on last menstrual period data of 282, 1,5 283, 6,17 and 284 4 days, respectively.…”

Reference intervals of gestational sac, yolk sac, embryonic length, embryonic heart rate at 6–10 weeks after in vitro fertilization-embryo transfer

“…Some researchers have suggested that the use of assisted reproduction data can improve dating accuracy; however, the accuracy is limited before 7 GW and is equivocal for menstrual dating beyond that GA [26], which may partly explain the considerable differences in CRL at day 45 between our study and previous studies. Additionally, CRL has been reported to overestimate gestation [27], and using CRL to determine GA has been reported to be less accurate than GA estimated by a certain LMP or day of oocyte retrieval in early pregnancy [28]; therefore, the CRL corresponding to the calculated GA is longer than the CRL of the same GA in IVF populations.…”